U.S. patent application number 15/406436 was filed with the patent office on 2017-07-20 for feedback-assisted rapid discharge heating and forming of metallic glasses.
The applicant listed for this patent is Glassimetal Technology, Inc.. Invention is credited to Marios D. Demetriou, William L. Johnson, Joseph P. Schramm.
Application Number | 20170203358 15/406436 |
Document ID | / |
Family ID | 59313494 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170203358 |
Kind Code |
A1 |
Schramm; Joseph P. ; et
al. |
July 20, 2017 |
FEEDBACK-ASSISTED RAPID DISCHARGE HEATING AND FORMING OF METALLIC
GLASSES
Abstract
The disclosure is directed to an apparatus comprising
feedback-assisted control of the heating process in rapid discharge
heating and forming of metallic glass articles.
Inventors: |
Schramm; Joseph P.; (Sierra
Madre, CA) ; Demetriou; Marios D.; (West Hollywood,
CA) ; Johnson; William L.; (San Marino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Glassimetal Technology, Inc. |
Pasadena |
CA |
US |
|
|
Family ID: |
59313494 |
Appl. No.: |
15/406436 |
Filed: |
January 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62278781 |
Jan 14, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22D 17/08 20130101;
B22D 21/005 20130101; B22D 17/32 20130101; B22D 25/06 20130101;
C21D 11/00 20130101; C22C 16/00 20130101; B21J 1/006 20130101; C21D
1/40 20130101 |
International
Class: |
B22D 21/00 20060101
B22D021/00; B22D 25/06 20060101 B22D025/06; B21J 1/00 20060101
B21J001/00; C22C 16/00 20060101 C22C016/00; H05B 3/00 20060101
H05B003/00; H05B 3/02 20060101 H05B003/02; B22D 17/08 20060101
B22D017/08; B22D 17/32 20060101 B22D017/32 |
Claims
1. A rapid discharge heating and forming (RDHF) apparatus
comprising: an electrical circuit comprising: a source of
electrical energy; a metallic glass sample; at least two electrodes
connecting the source of electrical energy to a sample of metallic
glass feedstock; a feedback control loop comprising: a
temperature-monitoring device disposed in temperature monitoring
relationship with the sample configured to generate a signal
indicative of the temperature of the sample; a computing device in
signal communication with the temperature-monitoring device
configured to convert the signal from the temperature-monitoring
device to a sample temperature T, compare T to a predefined
temperature value T.sub.o, and generate a current terminating
signal when T substantially matches T.sub.o; and a current
interrupting device electrically connected with the source of
electrical energy and in signal communication with the computing
device, and where the current interrupting device is configured to
terminate the electrical current generated by the source of
electrical energy when the current terminating signal is received
from the computing device; and a shaping tool disposed in forming
relation to the metallic glass sample.
2. The RDHF apparatus of claim 1, wherein the
temperature-monitoring device is selected from a group consisting
of thermocouple, pyrometer, thermographic camera, and resistance
temperature detector, or combinations thereof.
3. The RDHF apparatus of claim 1, wherein the current interrupting
device is selected from a group consisting of gate turn-off
thyristor, power metal oxide semiconductor field emission
transistor (MOSFET), integrated gate-commutated thyristor, and
insulated gate bipolar transistor, or combinations thereof.
4. The RDHF apparatus of claim 1, wherein the source of electrical
energy of the RDHF apparatus comprises a capacitor.
5. The RDHF apparatus of claim 1, wherein the shaping tool of the
RDHF apparatus comprises an injection mold.
6. The RDHF apparatus of claim 1, wherein the shaping tool of the
RDHF apparatus comprises an extrusion die.
7. The RDHF apparatus of claim 1, wherein the shaping tool of the
RDHF apparatus comprises a forging die.
8. The RDHF apparatus of claim 1, wherein the shaping tool of the
RDHF apparatus comprises a blow molding die.
9. The RDHF apparatus of claim 1, wherein the
temperature-monitoring device comprises a pyrometer coupled to a
fiber-optic feedthrough across a feedstock barrel that contains the
sample of metallic glass feedstock.
10. The RDHF apparatus of claim 1, wherein the
temperature-monitoring device comprises a thermocouple embedded in
a feedstock barrel containing the sample of the metallic glass
feedstock.
11. The RDHF apparatus of claim 1, wherein the
temperature-monitoring device comprises a resistive temperature
detector embedded in a feedstock barrel containing the sample of
the metallic glass feedstock.
12. A method of rapidly heating and shaping a metallic glass
comprising: discharging electrical energy uniformly through a
sample of metallic glass formed of a metallic glass forming alloy
to generate an electrical current that uniformly heats the sample;
monitoring the temperature of the sample; terminating the
electrical current when the temperature of the sample substantially
matches a predefined temperature T.sub.o, where T.sub.o is between
the glass transition temperature of the metallic glass and the
equilibrium melting point of the metallic glass forming alloy;
applying a deformational force to shape the heated sample into an
article; and cooling the article to a temperature below the glass
transition temperature of the metallic glass.
13. The method of claim 12, wherein the electrical energy
discharged ranges from 50 J to 100 kJ.
14. The method of claim 12, wherein the electrical energy is at
least 100 J and a discharge time constant of between 10 .mu.s and
100 ms.
15. The method of claim 12, wherein the processing temperature is
within 50 degrees of the half-way point between the glass
transition temperature of the metallic glass and the equilibrium
melting point of the metallic glass forming alloy.
16. The method of claim 12, wherein the predefined temperature
T.sub.o is such that the viscosity of the heated sample is from 1
to 10.sup.4 Pas-sec.
17. The method of claim 12, wherein the metallic glass is an alloy
based on an elemental metal selected from the group consisting of
Zr, Pd, Pt, Au, Fe, Co, Ti, Al, Mg, Ni and Cu.
18. The method of claim 12, wherein the step of discharging the
electrical energy generates a dynamic electrical field in the
sample, and wherein the electromagnetic skin depth of the dynamic
electric field generated is large compared to the radius, width,
thickness, and length of the sample.
19. The method of claim 12, wherein the shaping step is selected
from the group consisting of injection molding, forging, extrusion,
and blow molding.
20. The method of claim 12, wherein the heating rate is at least
500 K/s.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This patent application claims the benefit of U.S. patent
application Ser. No. 62/278,781, entitled "FEEDBACK-ASSISTED RAPID
DISCHARGE HEATING AND FORMING OF METALLIC GLASSES," filed on Jan.
14, 2016 under 35 U.S.C..sctn.119(e), which is incorporated herein
by reference in its entirety.
FIELD
[0002] The disclosure is directed to an apparatus including
feedback-assisted control of the heating process in rapid discharge
heating and forming (RDHF) of metallic glasses.
BACKGROUND
[0003] U.S. Pat. No. 8,613,813 entitled "Forming of Metallic Glass
by Rapid Capacitor Discharge" is directed, in certain aspects, to a
rapid discharge heating and forming method (RDHF method), in which
a metallic glass is rapidly heated and formed into an amorphous
article by discharging an electrical energy through a metallic
glass sample cross-section to rapidly heat the feedstock to a
process temperature in the range between the glass transition
temperature of the metallic glass and the equilibrium liquidus
temperature of the glass-forming alloy (termed the "undercooled
liquid region") and shaping and then cooling the sample to form an
amorphous article.
[0004] U.S. Pat. No. 8,613,813 is also directed, in certain
aspects, to a rapid discharge heating and forming apparatus (RDHF
apparatus), which includes a metallic glass feedstock, a source of
electrical energy, at least two electrodes interconnecting the
source of electrical energy to the metallic glass feedstock, where
the electrodes are attached to the feedstock such that connections
are formed between the electrodes and the feedstock, and a shaping
tool disposed in forming relation to the feedstock. In the
disclosed apparatus, the source of electrical energy is capable of
producing electrical energy uniformly through a sample such that
the generated electrical current heats the entirety of the sample
to a process temperature between the glass transition temperature
of the amorphous material and the equilibrium liquidus temperature
of the alloy, while the shaping tool is capable of applying a
deformational force to form the heated sample to a net shape
article.
BRIEF DESCRIPTION OF FIGURES
[0005] The description will be more fully understood with reference
to the following figures and data graphs, which are presented as
various embodiments of the disclosure and should not be construed
as a complete recitation of the scope of the disclosure.
[0006] FIG. 1 presents a plot of the viscosity of example metallic
glass Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 against
temperature in the undercooled liquid region (i.e. between the
glass-transition temperature, T.sub.g, and liquidus temperature,
T.sub.l, in accordance with embodiments of the disclosure.
[0007] FIG. 2 presents a plot of the time window of stability
against crystallization of example metallic glass
Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 against
temperature in the undercooled liquid region (i.e. between the
glass-transition temperature, T.sub.g, and liquidus temperature,
T.sub.l,) in accordance with embodiments of the disclosure.
[0008] FIG. 3 presents a schematic illustrating the RDHF electrical
circuit that includes the feedback control loop in accordance with
embodiments of the disclosure.
[0009] FIG. 4 is a schematic illustrating an RDHF apparatus
including a temperature-monitoring device in accordance with
embodiments of the disclosure.
[0010] FIG. 5 is a flow chart illustrating the steps of RDHF
methods including monitoring sample temperature in accordance with
embodiments of the disclosure.
BRIEF SUMMARY
[0011] The disclosure is directed to an apparatus including
feedback-assisted control of the heating process in rapid discharge
heating and forming of metallic glass articles.
[0012] In some embodiments, the disclosure is directed to an RDHF
apparatus including an electrical circuit that includes a source of
electrical energy, a metallic glass feedstock sample, at least two
electrodes interconnecting the source of electrical energy to the
sample, and a feedback control loop. The RDHF apparatus also
includes a shaping tool disposed in forming relation to the
sample.
[0013] The feedback control loop according to embodiments of the
disclosure includes a temperature-monitoring device, a computing
device, and a current interrupting device. The
temperature-monitoring device is disposed in temperature monitoring
relationship with the sample, and is configured to generate a
signal indicative of the temperature of the sample. The computing
device is in communication with the temperature-monitoring device,
and is configured to convert the signal from the
temperature-monitoring device to a sample temperature T, compare T
to a predefined temperature value T.sub.o, and generate a current
terminating signal when T substantially matches T.sub.o. The
current interrupting device is electrically connected with the
source of electrical energy and in signal communication with the
computing device. The current interrupting device is configured to
terminate (e.g., switch off) the electrical current generated by
the source of electrical energy when a current terminating signal
is received from the computing device.
[0014] In another embodiment, the temperature monitoring device is
selected from a group consisting of a thermocouple, a pyrometer,
thermographic camera, a resistance temperature detector, or
combinations thereof.
[0015] In another embodiment, the current interrupting device is
selected from a group consisting of a gate turn-off thyristor, a
power MOSFET (metal oxide semiconductor field emission transistor),
an integrated gate-commutated thyristor, and an insulated gate
bipolar transistor, or combinations thereof.
[0016] In another embodiment, the source of electrical energy of
the RDHF apparatus includes a capacitor.
[0017] In another embodiment, the electrical circuit of the RDHF
apparatus is a capacitive discharge circuit.
[0018] In another embodiment, the shaping tool of the RDHF
apparatus includes an injection mold, and monitoring of temperature
is achieved by the use of a pyrometer via a fiber-optic feedthrough
across the feedstock barrel.
[0019] In another embodiment, the shaping tool of the RDHF
apparatus includes an injection mold, and monitoring of temperature
is achieved by the use of a thermocouple or a resistive temperature
detector embedded in the feedstock barrel in proximity to the
feedstock.
[0020] Additional embodiments and features are set forth in part in
the description that follows, and will become apparent to those
skilled in the art upon examination of the specification or may be
learned by the practice of the disclosed subject matter. A further
understanding of the nature and advantages of the disclosure may be
realized by reference to the remaining portions of the
specification and the drawings, which forms a part of this
disclosure.
DETAILED DESCRIPTION
[0021] The disclosure is directed to an apparatus including
feedback-assisted control of the heating process in rapid discharge
heating and forming of metallic glass articles. In some
embodiments, the disclosure is directed to an RDHF apparatus
including an electrical circuit. The electrical circuit includes a
source of electrical energy, at least two electrodes
interconnecting the source of electrical energy to a metallic glass
feedstock sample, and a feedback control loop. The RDHF apparatus
also includes a shaping tool disposed in forming relation to the
sample. The feedback control loop can comprise a
temperature-monitoring device disposed in a temperature monitoring
relationship with the sample configured to generate a signal
indicative of the temperature of the sample; a computing device in
communication with the temperature-monitoring device and configured
to convert the signal from the temperature monitoring device to a
sample temperature T, compare T to a predefined temperature value
T.sub.o, and generate a current terminating signal when T
substantially matches T.sub.o; and a current interrupting device
electrically connected with the source of electrical energy and in
signal communication with the computing device, and where the
current interrupting device is configured to terminate (e.g.,
switch off) the electrical current generated by the source of
electrical energy when a current terminating signal is received
from the computing device.
[0022] The RDHF process involves rapidly discharging electrical
current across a metallic glass feedstock via electrodes in contact
with the feedstock in order to rapidly and uniformly heat the
feedstock to a temperature conducive for viscous flow. A
deformational force is applied to the heated and softened feedstock
to deform the heated feedstock into a desirable shape. The steps of
heating and deformation are performed over a time scale shorter
than the time required for the heated feedstock to crystallize.
Subsequently, the deformed feedstock is allowed to cool to below
the glass transition temperature, typically by contact with a
thermally conductive metal mold or die in order to vitrify it into
an amorphous article.
[0023] RDHF techniques are methods of uniformly heating a metallic
glass rapidly using Joule heating (e.g. heating times of less than
1 s, and in some embodiments less than 100 milliseconds), softening
the metallic glass, and shaping it into a net shape article using a
shaping tool (e.g. an extrusion die or a mold). In some
embodiments, the methods can utilize the discharge of electrical
energy (e.g. 50 J to 100 kJ) stored in an energy source to
uniformly and rapidly heat a sample of a metallic glass to a
"process temperature" between the glass transition temperature
T.sub.g of the metallic glass and the equilibrium melting point of
the metallic glass forming alloy T.sub.m on a time scale of several
milliseconds or less, and is referred to hereinafter as rapid
discharge heating and forming (RDHF).
[0024] An "RDHF apparatus," as disclosed in U.S. Pat. No.
8,613,813, includes a metallic glass feedstock, a source of
electrical energy, at least two electrodes interconnecting the
source of electrical energy to the metallic glass feedstock where
the electrodes are attached to the feedstock such that connections
are formed between electrodes and feedstock, and a shaping tool
disposed in forming relation to the feedstock. In some embodiments,
the metallic glass feedstock can have a uniform cross-section. The
feedstock having a uniform cross-section means that the
cross-section along the length of the feedstock does not vary by
more than 20%. In other embodiments, the feedstock having a uniform
cross-section means that the cross-section along the length of the
feedstock does not vary by more than 10%. In yet other embodiments,
the feedstock having a uniform cross-section means that the
cross-section along the length of the feedstock does not vary by
more than 5%. In yet other embodiments, the feedstock having a
uniform cross-section means that the cross-section along the length
of the feedstock does not vary by more than 1%.
[0025] In some embodiments, the source of electrical energy
includes a capacitor. In some embodiments, the source of electrical
energy includes a capacitor connected to at least one current
interrupting device selected from a gate turn-off thyristor, a
power MOSFET (metal oxide semiconductor field emission transistor),
an integrated gate-commutated thyristor, and an insulated gate
bipolar transistor. In some embodiments, the shaping tool is
selected from the group consisting of an injection mold, a dynamic
forge, a stamp forge and a blow mold. In some embodiments, the
shaping tool is operated by a pneumatic drive, magnetic drive, or
electrical drive. An "RDHF apparatus" where the shaping tool is an
injection mold, as disclosed in U.S. Patent Application Publication
No. 2013/0025814, also includes a "feedstock barrel" to
electrically insulate and mechanically confine the feedstock.
[0026] In the RDHF process, controlling the heating of the
feedstock such that the feedstock reaches a selected process
temperature in the undercooled liquid region is important, because
the temperature of the feedstock in the undercooled liquid region
determines the viscosity of the feedstock and the time window in
which the feedstock is stable against crystallization. The
viscosity and time window of stability against crystallization are,
in turn, critical in determining the success of the RDHF process.
In some embodiments of the RDHF process, the viscosity is in the
range of 10.sup.0to 10.sup.4 Pa-s, while in other embodiments, the
viscosity is in the range of 10.sup.1 to 10.sup.3 Pa-s. If the
viscosity is very high (i.e. higher than 10.sup.4 Pa-s), a high
pressure may be needed in order to shape the undercooled liquid and
form an amorphous article. On the other hand, if the viscosity is
very low (i.e. lower than 10.sup.0Pa-s), the shaping process may
become unstable causing flow instabilities that may result in
structural and cosmetic defects in the amorphous article. The time
window of stability against crystallization must be large enough
that the heating and forming process are completed prior to the
onset of crystallization. In some embodiments of the RDHF process
the time window of stability against crystallization is at least 10
ms, while in other embodiments the time window is at least 100
ms.
[0027] Both the viscosity and the time window of stability against
crystallization may vary over many orders of magnitude against
temperature in the undercooled liquid region. Specifically, the
viscosity varies hyper-exponentially while the time window of
stability against crystallization varies exponentially against
temperature. As shown in FIG. 1, the viscosity of example metallic
glass Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 varies
by about 12 orders of magnitude against temperature in the
undercooled liquid region (i.e. between the glass-transition
temperature, T.sub.g, and liquidus temperature, T.sub.l) (the data
in FIG. 1 are taken from A. Masuhr, T. A. Waniuk, R. Busch, W. L.
Johnson, Phys. Rev. Lett. 82, 2290 (1999), the disclosure of which
is incorporated herein by reference). And as shown in FIG. 2, the
time window of stability against crystallization of example
metallic glass
Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 varies by
about at least 3 orders of magnitude against temperature in the
undercooled liquid region (i.e. between the glass-transition
temperature, T.sub.g, and liquidus temperature, T.sub.l) (the data
in FIG. 2 are taken from Schroers, A. Masuhr, W. L. Johnson, R.
Busch, Phys. Rev. B 60, 11855 (1999), the disclosure of which is
incorporated herein by reference). Because both variables, i.e.
viscosity and time window of stability against crystallization,
vary strongly (i.e. exponentially or hyper-exponentially) with
temperature in the undercooled liquid region, accurate control of
the heating in the RDHF process such that a target process
temperature may be attained associated with a desired viscosity and
time window of stability against crystallization is important.
[0028] In conventional RDHF apparatuses where the source of
electrical energy includes a capacitor, heating of the feedstock or
feedstock sample to attain a certain process temperature may be
controlled by adjusting the voltage of the capacitors. By setting a
certain discharge voltage V in a capacitive discharge circuit of
capacitance C, a certain electrical current I is discharged through
the RDHF circuit, and an associated electrical energy is dissipated
within the resistors in the RDHF circuit. The total dissipated
electrical energy E.sub.t may be approximated by the relation
E.sub.t.apprxeq.0.5CV.sup.2. A part of the energy E.sub.t is
dissipated within the feedstock, denoted as E. The fraction
E/E.sub.t may be related to the ratio of the feedstock resistance,
denoted as R, over the total resistance of the RDHF electrical
circuit 300 (including the resistance of feedstock sample 302),
denoted as R.sub.t ,i.e. E/E.sub.t.apprxeq.R/R.sub.t . Part of the
energy E dissipated within the feedstock sample 302 is used to heat
the feedstock sample 302 from an initial sample temperature T.sub.i
to a final sample temperature T, while another part is absorbed at
the glass transition as recovery enthalpy. The energy dissipated
within the feedstock E may be approximately related to the
feedstock process temperature T according to
E=.OMEGA..intg.c.sub.pdT, where c.sub.p is the temperature
dependent heat capacity of the feedstock in J/m.sup.3-K, .OMEGA. is
the volume of the feedstock in m.sup.3, .DELTA.H is the recovered
enthalpy during the glass transition of the feedstock, and
.intg.c.sub.pdT is the temperature integral of c.sub.p from an
initial feedstock temperature T.sub.i to a final process
temperature T. Substituting the approximate relations for E and
E/E.sub.t and solving for V, one may arrive at the following
approximate relation between V and T:
V= [2(.intg.c.sub.pdT).OMEGA.R.sub.t/RC] EQ. (1)
[0029] In theory, EQ. (1) above may be used to determine the
voltage V in order to heat the feedstock from an initial
temperature T.sub.i to a final process temperature T provided that
.OMEGA., R.sub.t, R, C, and c.sub.p as a function of temperature,
i.e. c.sub.p(T), are known. In practice though, this equation is
difficult to solve accurately, because c.sub.p(T) is a complicated
function involving different temperature dependencies below and
above the glass-transition temperature T.sub.g (i.e. in the glass
and liquid states), and a recovery enthalpy at T.sub.g. The
recovery enthalpy at T.sub.g is actually a function of T.sub.g, and
T.sub.g itself is a function of the heating rate through the glass
transition. Approximations can be made for .intg.c.sub.pdT, but
these approximations are generally not completely accurate. As
such, the accuracy and overall utility of EQ. (1) in predicting the
voltage V to achieve a desired feedstock process temperature T is
quite limited. Accordingly, EQ. (1) may only be useful as a guide,
and precise heating to a desired feedstock temperature T may only
be achieved iteratively by conducting several experiments to
determine the corresponding V.
[0030] Hence an RDHF apparatus with a capability to accurately
control the heating of the feedstock such that an appropriate
feedstock process temperature T can be achieved is desirable. The
disclosure is directed to an apparatus including feedback-assisted
control of the heating process in rapid discharge heating and
forming of metallic glass articles.
[0031] In some embodiments, the disclosure is directed to an RDHF
apparatus including an electrical circuit that includes a feedback
control loop. FIG. 3 presents a schematic of the RDHF electrical
circuit that includes a feedback control loop in accordance with
embodiments of the disclosure. The RDHF electrical circuit 300
includes a metallic glass feedstock sample 302 and an energy source
304 electrically connected to the sample 302 through electrodes
316. The electrical circuit 300 provides an electrical current 312.
The RDHF electrical circuit 300 also includes a current
interrupting device 310 electrically connected between the sample
302 and the energy source 304. A feedback control loop 314 within
the RDHF electrical circuit 300 includes a temperature-monitoring
device 306 disposed in temperature monitoring relationship with the
sample 302; and a computing device 308 in signal communication with
the temperature-monitoring device 306 and current interrupting
device 310. The computing device 308 is configured to receive an
input signal from the temperature-monitoring device 306 and to also
send an output signal to the current-interrupting device 310.
Specifically, the computing device 308 is configured to convert a
signal from the temperature-monitoring device 306 to a sample
temperature T, compare the sample temperature T to a predefined
temperature value T.sub.o, and send an activation signal to
activate the current-interrupting device 310 when the sample
temperature T substantially matches the predefined temperature
value T.sub.o. When activated, the current interrupting device 310
terminates (e.g., switches off) the electrical current through the
RDHF electrical circuit 300 such that the heating process is
terminated and the predefined temperature value T stabilizes
substantially close to the predefined temperature value
T.sub.o.
[0032] In the context of the disclosure, a "temperature-monitoring
device" means a device capable of real-time monitoring or measuring
of the temperature of the feedstock. In various embodiments, a
"temperature-monitoring device" can be a thermocouple, a pyrometer,
thermographic camera, a resistance temperature detector, or
combinations thereof. In some embodiments, the response time of the
"temperature monitoring device" is less than 10 ms, while in other
embodiments less than 1 ms, while in other embodiments less than
0.1 ms, while in yet other embodiments less than 0.01 ms.
[0033] In the context of the disclosure, a "computing device" means
a device capable of being programmed to carry out a set of
arithmetic or logical operations automatically.
[0034] In the context of the disclosure, a "current interrupting
device" means a device electrically connected with the source of
electrical energy capable of terminating or terminates (e.g.,
switches off) the electrical current passing through the RDHF
circuit, including the feedstock, when activated by a signal. In
some embodiments, the current interrupting device is a gate
turn-off thyristor, a power MOSFET (metal oxide semiconductor field
emission transistor), an integrated gate-commutated thyristor, an
insulated gate bipolar transistor, or combinations thereof. In some
embodiments, the response time of the "current interrupting device"
is less than 1 ms, while in other embodiments less than 0.1 ms,
while in other embodiments less than 0.01 ms, while in yet other
embodiments less than 0.001 ms.
[0035] In some embodiments of the disclosure, "T substantially
matches T.sub.o" means the value of T is within 10% of T.sub.o
where T and T.sub.o are in absolute "Kelvin" units. In one
embodiment, "T substantially matches T.sub.o" means the value of T
is within 5% of T.sub.o, where T and T.sub.o are in absolute
"Kelvin" units. In another embodiment, "T substantially matches
T.sub.o" means the value of T is within 3% of T.sub.o where T and
T.sub.o are in absolute "Kelvin" units. In another embodiment "T
substantially matches T.sub.o" means the value of T is within 2% of
T.sub.o, where T and To are in absolute "Kelvin" units. In yet
another embodiment "T substantially matches T.sub.o" means the
value of T is within 1% of T.sub.o where T and T.sub.o are in
absolute "Kelvin" units.
[0036] In other embodiments of the disclosure, "T substantially
matches T.sub.o" means the absolute difference between T and
T.sub.o is not more than 20.degree. C. In one embodiment, "T
substantially matches T.sub.o" means the absolute difference
between T and T.sub.ois not more than 10.degree. C. In another
embodiment, "T substantially matches T.sub.o" means the absolute
difference between T and T.sub.o is not more than 5.degree. C. In
another embodiment "T substantially matches T.sub.o" means the
absolute difference between T and T.sub.o is not more than
2.degree. C. In yet another embodiment "T substantially matches
T.sub.o" means the absolute difference between T and T.sub.o is not
more than 1.degree. C.
[0037] In other embodiments, the shaping tool of the RDHF apparatus
may be an injection mold, and the temperature-monitoring device can
monitor the sample temperature via a fiber-optic feedthrough across
the feedstock barrel.
[0038] In other embodiment, the shaping tool of the RDHF apparatus
may be a blow-molding die, a forging die, or an extrusion die. In
other embodiments, any source of electrical energy suitable for
supplying sufficient energy to rapidly and uniformly heat the
sample 302 to a process temperature T. In one embodiment, the
energy source 304 may include a capacitor having a discharge time
constant of from 10 .mu.s to 100 ms.
[0039] The electrodes 306 may be any electrically conducting
electrodes suitable for providing uniform contact across the sample
302 and electrically connect the sample to the energy source 304.
In one embodiment, the electrodes are formed of a an electrically
conducting metal, such as, for example, Ni, Ag, Cu, or alloys made
using at least 95 at % of Ni, Ag and Cu.
[0040] Turning to the shaping method itself, a schematic of an
exemplary shaping tool representing an injection mold in accordance
with the RDHF method of the disclosure is provided in FIG. 4. In
one embodiment, shown schematically in FIG. 4, a system 400
represents an injection molding shaping tool in accordance with the
RDHF method. As shown, the basic RDHF injection mold includes a
sample 402, held between a mechanically loaded plunger 420, which
also acts as the top electrode, and rests on an electrically
grounded base electrode 416. The plunger 420 may also act as the
top electrode, and may be made of a conducting material (such as
copper or silver) having both high electrical conductivity and
thermal conductivity. The sample 402 is contained within a "barrel"
or "shot sleeve" 422 that electrically insulates the sample 402
from a mold 424, and is in fluid communication with a mold cavity
418 contained within the mold 424. In such an embodiment, the
electrical current provided to the RDHF electrical circuit is
discharged uniformly through the metallic glass sample 402 provided
that certain criteria discussed above are met. The loaded plunger
420 then drives the viscous melt of the heated sample 402 such that
the melt is is injected into the mold cavity to form a net shape
component of the metallic glass.
[0041] The RDHF method sets forth two criteria, which must be met
to prevent the development of a temperature inhomogeneity thus
ensuring uniform heating of the sample: uniformity of the current
within the sample; and stability of the sample with respect to
development of inhomogeneity in power dissipation during dynamic
heating.
[0042] Although these criteria seem relatively straightforward,
they place a number of physical and technical constraints on the
electrical charge used during heating, the material used for the
sample, the shape of the sample, and the interface between the
electrode used to introduce the charge and the sample itself.
[0043] Uniformity of the current within the sample during capacity
discharge requires that the electromagnetic skin depth of the
dynamic electric field is large compared to relevant dimensional
characteristics of the sample (radius, length, width or thickness).
In the example of a cylindrical sample, the relevant characteristic
dimensions would obviously be the radius and length of the sample,
R and L. Hence, uniform heating within a cylindrical sample may be
achieved when the electromagnetic skin depth of the dynamic
electric field is greater than R and L.
[0044] A simple flow chart of the RDHF technique of the disclosure
is provided in FIG. 5. As shown, the RDHF process begins with
providing a sample of metallic glass having a uniform cross-section
at operation 502.
[0045] The process begins with the discharge of electrical energy
(in some embodiments in the range of 50 J to 100 KJ) stored in a
source of electrical energy (in some embodiments the source of
electrical energy may be a capacitor) into a metallic glass sample
at operation 504. In accordance with the disclosure, the
application of the electrical energy may be used to rapidly and
uniformly heat the sample to a predefined "process temperature"
T.sub.o above the glass transition temperature of the alloy (in
some embodiments T.sub.o is within 50 degrees of the half-way point
between the glass transition temperature of the metallic glass and
the equilibrium melting point of the metallic glass forming alloy;
in other embodiments, T.sub.o is about 200-300 K above T.sub.g), on
a time scale of several microseconds (in some embodiments in the
range of 1 ms to 100 ms), achieving heating rates sufficiently high
to suppress crystallization of the alloy at that temperature (in
some embodiment, the heating rates are at least 500 K/s). The
predefined temperature T.sub.o is determined to be a temperature
where the viscous metallic glass alloy has a process viscosity
conducive to thermoplastic shaping (in some embodiments in the
range of 1 to 10.sup.4 Pa-s).
[0046] Following the discharge of electrical energy, the RDHF
process also includes monitoring the temperature of the sample Tat
operation 506 by generating a signal indicative of T. The sample
temperature monitoring may be performed by a temperature-monitoring
device as described earlier. The RDHF process also includes
comparing the temperature of the sample to a predefined temperature
at operation 508.
[0047] The RDHF process further includes converting a signal from
the temperature-monitoring device to a sample temperature T,
comparing T to a predetermined temperature value T.sub.o and
generating a current terminating signal when T substantially
matches the predefined process temperature T.sub.o. The signal
conversion and comparison processes can be performed by the
computing device, as described herein.
[0048] The RDHF process further includes terminating (e.g.,
switching off) the electrical current generated by the source of
electrical energy when a current terminating signal is received at
operation 510. The current termination process can be performed by
a current terminating device as described earlier.
[0049] Once the current is terminated after the sample reaches a
uniform temperature that substantially matches the predefined
process temperature T.sub.o, the RDHF process may also include
shaping of the viscous sample into an amorphous bulk article at
operation 512.
[0050] Lastly, the RDHF process may also include cooling the
article below the glass transition temperature of the metallic
glass sample at operation 514. In some embodiments, the shaping and
cooling steps are performed simultaneously.
[0051] In some embodiments, the present feedback control loop can
be incorporated into the electrical circuit of any existing rapid
capacitive discharging forming (RCDF) apparatus, such as disclosed
in the following patents or patent applications: U.S. Pat. No.
8,613,813, entitled "Forming of metallic glass by rapid capacitor
discharge;" U.S. Pat. No. 8,613,814, entitled "Forming of metallic
glass by rapid capacitor discharge forging"; U.S. Pat. No.
8,613,815, entitled "Sheet forming of metallic glass by rapid
capacitor discharge;" U.S. Pat. No. 8,613,816, entitled "Forming of
ferromagnetic metallic glass by rapid capacitor discharge;" U.S.
9,297,058, entitled "Injection molding of metallic glass by rapid
capacitor discharge;" each of which is incorporated by reference in
its entirety.
[0052] The RDHF shaping techniques and alternative embodiments
discussed above may be applied to the production of complex, net
shape, high performance metal components such as casings for
electronics, brackets, housings, fasteners, hinges, hardware, watch
components, medical components, camera and optical parts, jewelry
etc. The RDHF method can also be used to produce sheets, tubing,
panels, etc., which could be shaped through various types of molds
or dies used in concert with the RDHF apparatus.
[0053] The methods and apparatus herein can be valuable in the
fabrication of electronic devices using bulk metallic glass
articles. In various embodiments, the metallic glass may be used as
housings or other parts of an electronic device, such as, for
example, a part of the housing or casing of the device. Devices can
include any consumer electronic device, such as cell phones,
desktop computers, laptop computers, and/or portable music players.
The device can be a part of a display, such as a digital display, a
monitor, an electronic-book reader, a portable web-browser, and a
computer monitor. The device can also be an entertainment device,
including a portable DVD player, DVD player, Blue-Ray disk player,
video game console, music player, such as a portable music player.
The device can also be a part of a device that provides control,
such as controlling the streaming of images, videos, sounds, or it
can be a remote control for an electronic device. The alloys can be
part of a computer or its accessories, such as the hard driver
tower housing or casing, laptop housing, laptop keyboard, laptop
track pad, desktop keyboard, mouse, and speaker. The metallic glass
can also be applied to a device such as a watch or a clock.
[0054] Having described several embodiments, it will be recognized
by those skilled in the art that various modifications, alternative
constructions, and equivalents may be used without departing from
the spirit of the disclosure. Additionally, a number of well-known
processes and elements have not been described in order to avoid
unnecessarily obscuring the embodiments disclosed herein.
Accordingly, the above description should not be taken as limiting
the scope of the document.
[0055] Those skilled in the art will appreciate that the presently
disclosed embodiments teach by way of example and not by
limitation. Therefore, the matter contained in the above
description or shown in the accompanying drawings should be
interpreted as illustrative and not in a limiting sense. The
following claims are intended to cover all generic and specific
features described herein, as well as all statements of the scope
of the present method and and system, which, as a matter of
language, might be said to fall therebetween.
* * * * *